Surface treatment chemical and bath for forming hydrophilic coatings and method of surface-treating aluminum members

ABSTRACT

Surface treatment chemical and bath for forming hydrophilic coatings on aluminum plates comprising, on a solid basis, 5-25 parts by weight of a sodium salt and/or a potassium salt of carboxymethylcellulose, and 25-50 parts by weight of an ammonium salt of carboxymethylcellulose, and 25-70 parts by weight of N-methylol acrylamide, which may further contain 1.5-15 parts by weight of polyacrylic acid and 0.6-9 parts by weight (as Zr) of a zirconium compound, per 100 parts by weight of the above indispensable components.

BACKGROUND OF THE INVENTION

The present invention relates to an aqueous surface treatment chemicalfor forming hydrophilic coatings on heat exchanger fins, etc., a bathcontaining such a surface treatment chemical, a method ofsurface-treating an aluminum member with such an aqueous surfacetreatment chemical, and an aluminum member provided with a hydrophiliccoating of such a surface treatment chemical. More particularly, itrelates to an aqueous surface treatment chemical for forming hydrophiliccoatings with good corrosion resistance and highly durable hydrophilicnature and also with no or extremely reduced odor on aluminum fins ofheat exchangers, a bath containing such a surface treatment chemical anda method of treating them.

Aluminum and its alloys are light and have good workability and heatconductance, so that they are widely used for fins of heat exchangers.Recently more and more air conditioners have been used not only forcooling but also for warming and dehumidification. In heat exchangeparts of these air conditioners, aluminum alloy fins are generally used.

However, it is observed that moisture tends to be condensed anddeposited as water droplets on the fin surfaces of air conditionersduring cooling operations. If the fin surface is water-repellent, thiscondensed water tends to be deposited in a hemispherical form on the finsurface or forms bridges between the fins, preventing smooth air flow,which in turn increases resistance of air flow, thereby decreasing heatexchange efficiency.

In addition, although aluminum and its alloys are essentially excellentin corrosion resistance, it is likely that the condensed water remainingon the aluminum fin surfaces for a long period of time functions like anoxygen concentration cell, and that contaminants such as nitrogen oxidesNO_(x) and sulfur oxides in the air are absorbed and concentrated in thecondensed water. As a result, a hydration reaction and a corrosionreaction are accelerated. Those produced by the corrosion areaccumulated on the aluminum fin surfaces, which not only deteriorateheat exchange performance, but also are blown out of the airconditioners as white fine powders together with a hot air during thewarming operation in the winter.

To solve these problems, various attempts have been made to form onaluminum fin surfaces coatings for improving their corrosion resistanceand for increasing their hydrophilic nature.

Such coatings are generally classified into inorganic coatings andorganic coatings.

Proposed as methods for forming inorganic coatings are methodscomprising forming a corrosion-resistant coating, for instance, by achromate treatment, and dipping it in an aqueous solution mainlycomposed of boehmite (Japanese Patent Laid-Open No. 56-b 108071), orsilicate to form a hydrophilic coating (Japanese Patent Laid-Open Nos.56-13078 and 50-38645). However, despite the fact that such inorganiccoatings have good corrosion resistance, they are poor in hydrophilicnature. Besides, in the case of a silicate treatment, it generatesunpleasant odor peculiar to silica. In addition, when it is used toproduce pre-coated coils, the coating is cracked while cutting so thatits corrosion resistance is reduced, and also severe tool wear takesplace by cutting operation of such precoated aluminum plates.

On the other hand, as a method of forming organic coating, a method offorming a hydrophilic coating on an aluminum surface by applying anaqueous solution comprising a water-soluble or water-dispersible,high-molecular weight resin and silica fine powders to the aluminumsurface, and then heatcuring the coating was proposed (for instance,Japanese Patent Laid-Open Nos. 55-99976, 53-125437 and 55-164264).However, since this coating contains fine silica powder, it suffers fromcracking while cutting in the case of a pre-coated aluminum plate,leading to lower corrosion resistance. And tools are extremely wornduring cutting operations and the coating has relatively poorhydrophilic nature. In addition, it causes air conditioners to releaseunacceptable if slight odor peculiar to silica. Incidentally, JapanesePatent Laid-Open No. 55-164264 discloses the use of water solublemelamines, alkyds, polyesters, acrylics for the same purpose, but theirproperties are not sufficient.

Further, U.S. Pat. No. 4,503,907 discloses a heat exchanger coated withan aqueous coating composition comprising a plurality of spaced finswith narrow distance in parallel to form flow passages between fins anda plurality of heat transfer pipes passing through the fins, the bothsurfaces of the fins being coated with an aqueous coating compositioncomprising 100 parts by weight of a resin component for water paint insolid content, 5 to 95 parts by weight of a surfactant and 5 to 65 partsby weight of synthetic silica and baked at a temperature of 120° C. to200° C. for 10 to 40 minutes for curing to give a coating film of 3 to20 μm, whereby the fins are provided with hydrophilic surfaces havingexcellent corrosion resistance and surface hardness. However, thiscoating composition also contains silica which causes the generation ofunacceptable odor.

U.S. Pat. No. 4,588,025 discloses a heat exchanger made of aluminum andcomprising a tube and fins attached to the tube, the heat exchangerbeing characterized in that the fins are treated with a coatingcomposition comprising an alkali silicate, a low-molecular weight,organic compound having carbonyl group, and a water-soluble,high-molecular weight organic compound, and are thereafter dried byheating, whereby a hydrophilic coating is formed over the surfaces ofthe fins. This hydrophilic coating too releases unacceptable odorbecause of the silicate.

Further, Japanese Patent Laid-Open No. 61-101798 discloses a heatexchanger fin constituted by a thin aluminum plate, which is coated witha first layer made of a water-soluble acrylic resin, and a second layermade of a water-soluble cellulose resin. However, it shows poor waterdissolution resistance.

In addition, Japanese Patent Laid-Open No. 62-105629 discloses analuminum heat exchanger fin coated with a corrosion-resistant layercomprising an organic layer made of a water-soluble acrylic resin or awater-soluble urethane resin or an inorganic layer made of a chromatelayer, a boehmite layer or an anodized layer, and a hydrophilic layerformed thereon, which comprises one or more organic compounds selectedfrom water-soluble cellulose resins and polyvinyl alcohol and a curingagent such as melamine resins. However, this hydrophilic coating is alsoinsufficient in hydrophilic nature and water dissolution resistance.

As described above, the conventional surface treatments of heatexchanger fins fail to provide surface coatings having sufficienthydrophilic nature and corrosion resistance and high mechanical strengthwithout generating unacceptable odor.

OBJECT AND SUMMARY OF THE INVENTION

An object of the present invention is, therefore, to provide an aqueoussurface treatment chemical for forming a hydrophilic coatings havingexcellent hydrophilic nature, corrosion resistance, water dissolutionresistance and solvent resistance with substantially no odor, on heatexchanger fins, etc.

Another object of the present invention is to provide a surfacetreatment bath containing such a surface treatment chemical.

A further object of the present invention is to provide a method forforming a hydrophilic coating with such properties or an aluminummember.

A still further object of the present invention is to provide an aqueoussurface treatment chemical for forming hydrophilic coating having notonly the above properties but also highly improved alkali resistance, sothat they can be formed on heat exchanger fins, etc. constituted bypre-coated aluminum plates, which require periodic rinsing with analkali solution at least once or twice a year.

A still further object of the present invention is to provide a surfacetreatment bath containing such a surface treatment chemical.

A still further object of the present invention is to provide a methodof forming such hydrophilic coatings with improved alkali resistance onan aluminum member.

A still further object of the present invention is to provide analuminum member provided with a hydrophilic coating having goodhydrophilic nature, corrosion resistance, water dissolution resistance,and solvent resistance with substantially no odor.

Thus, the first surface treatment chemical for forming a hydrophiliccoating according to the present invention comprises, on a solid basis,5-25 parts by weight of a sodium salt and/or a potassium salt ofcarboxymethylcellulose, 25-50 parts by weight of an ammonium salt ofcarboxymethylcellulose, and 25-70 parts by weight of N-methylolacrylamide.

The second surface treatment chemical for forming a hydrophilic coatingaccording to the present invention comprises, on a solid basis, 5-25parts by weight of a sodium salt and/or a potassium salt ofcarboxymethylcellulose, 25-50 parts by weight of an ammonium salt ofcarboxymethylcellulose, 25-70 parts by weight of N-methylol acrylamide,and further, per 100 parts by weight of (the sodium salt and/or thepotassium salt of carboxymethylcellulose + the ammonium salt ofcarboxymethylcellulose + the N-methylol acrylamide) , 1.5-15 parts byweight of polyacrylic acid and 0.6-9 parts by weight (as Zr) of azirconium compound.

The first method of suface-treating an aluminum member according to thepresent invention comprises the steps of degreasing the aluminum member,subjecting it to a chemical treatment, and then treating it with thefirst surface treatment chemical for forming a hydrophilic coating onthe aluminum member which comprises 5-25 parts by weight of a sodiumsalt and/or a potassium salt of a carboxymethylcellulose, 25-50 parts byweight of an ammonium salt of carboxymethylcellulose, and 25-70 parts byweight of N-methylol acrylamide.

The second method of surface-treating an aluminum member according tothe present invention comprises the steps of degreasing and thentreating it with the second surface treatment chemical comprising, on asolid basis, 5-25 parts by weight of a sodium salt and/or a potassiumsalt of carboxymethylcellulose, 25-50 parts by weight of an ammoniumsalt of carboxymethylcellulose, 25-70 parts by weight of N-methylolacrylamide, and further, per 100 parts by weight of (the sodium saltand/or the potassium salt of carboxymethylcellulose + the ammonium saltof carboxymethylcellulose + the N-methylol acrylamide), 1.5-15 parts byweight of polyacrylic acid and 0.6-9 parts by weight (as Zr) of azirconium compound.

The third method of surface-treating an aluminum member according to thepresent invention comprises the steps of degreasing it, subjecting it toa chemical treatment, and then treating it with the second surfacetreatment chemical comprising, on a solid basis, 5-25 parts by weight ofa sodium salt and/or a potassium salt of carboxymethylcellulose, 25-50parts by weight of an ammonium salt of carboxymethylcellulose, 25-70parts by weight of N-methylol acrylamide, and further, per 100 parts byweight of (the sodium salt and/or the potassium salt ofcarboxymethylcellulose + the ammonium salt of carboxymethylcellulose +the N-methylol acrylamide), 1.5-15 parts by weight of polyacrylic acidand 0.6-9 parts by weight (as Zr) of a zirconium compound.

Further, according to the present invention, there are provided surfacetreatment baths having the compositions as described above, and aluminummembers provided with hydrophilic coatings having the compositions asdescribed above.

DETAILED DESCRIPTION OF THE INVENTION

Carboxymethylcellulose used as a sodium salt, a potassium salt or anammonium salt generally has a polymerization degree of 30-800. When itsdegree of polymerization is less than 30, the resulting salt does nothave a sufficient water dissolution resistance, and when it exceeds 800,it has a too high viscosity, leading to poor coating characteristics.The preferred degree of polymerization of the carboxymethylcellulose is80-500.

The sodium salt and the potassium salt of carboxymethylcellulose serveto provide the coating layer with a hydrophilic nature. To provide thisfunction effectively, the sodium salt and/or the potassium salt ofcarboxymethylcellulose is 5-25 parts by weight on a solid basis in thesurface treatment chemical. When it is less than 5 parts by weight, itfails to give high hydrophilic nature expressed by a contact angle ofwater, and when it exceeds 25 parts by weight, the problem ofunacceptable odor is caused. The preferred amount of the sodium saltand/or the potassium salt of carboxymethylcellulose is 9-16 parts byweight.

The ammonium salt of carboxymethylcellulose has a function to reduceunacceptable odor. To achieve this function effectively, the NH₄ salt ofcarboxymethylcellulose is 25-50 parts by weight on a solid basis in thesurface treatment chemical. When it is less than 25 parts by weight,sufficient odor reduction effect cannot be obtained, and when it exceeds50 parts by weight, the hydrophilic nature of the resulting coatinglayer decreases. The preferred amount of the NH₄ salt ofcarboxymethylcellulose is 30-45 parts by weight.

A weight ratio of the Na salt and/or the K salt ofcarboxymethylcellulose to the NH₄ salt is 0.1:1-1:1. When the weightratio of the Na salt and/or the K salt to the NH₄ salt is less than 0.1,sufficient hydrophilic nature cannot be obtained, and when it exceeds 1,sufficient odor reduction effect cannot be obtained. The preferredweight ratio of the Na salt and/or the K salt to the NH₄ salt is0.2-0.53.

N-methylol acrylamide has a function to improve adhesion of theresulting hydrophilic coating to an aluminum surface and also toincrease coating's water dissolution resistance. The amount ofN-methylol acrylamide is 25-70 parts by weight on a solid basis in thesurface treatment chemical. When it is less than 25 parts by weight, theresulting coating does not show sufficient adhesion to an aluminumsurface and sufficient water dissolution resistance. On the other hand,when it exceeds 70 parts by weight, the hydrophilic nature of thecoating decreases. Incidentally, a weight ratio of the Na salt and/orthe K salt of carboxymethylcellulose + the NH₄ salt ofcarboxymethylcellulose to N-methylol acrylamide is 0.43-3.0. When it isless than 0.43, sufficient hydrophilic nature cannot be obtained, andwhen it exceeds 3.0, the resulting coating has poor adhesion to analuminum surface and poor water dissolution resistance. The preferredweight ratio is 0.64-1.56.

The surface treatment chemical for forming a hydrophilic coatingaccording to the present invention may contain, in addition to the aboveindispensable components, surfactants, anti-mold agents, antiseptics,etc.

The surfactants may be nonionic, cationic or anionic, but anionicsurfactants are preferable from the viewpoint of durability ofhydrophilic nature and the easiness of coating. Anionic surfactantswhich may be used include sodium alkylbenzene sulfonate, sodiumalkyldiphenylether disulfonate, sodium alkylnaphthalene sulfonate, asodium salt of naphthalenesulfonic acid-formalin condensate, etc. Theamount of anionic surfactants added is 1-10 parts by weight. When it isless than 1 part by weight, sufficient effect cannot be obtained by theaddition of anionic surfactants, and when it exceeds 10 parts by weight,the water dissolution resistance of the resulting coating decreases.

The anti-mold agents and the antiseptics may be quarternary ammoniumsalts, nitrogen-containing sulfur compounds, halogen-containing nitrogensulfide compounds, 1,2-benzisothiazoline-3-on (BIT), organic iodinecompounds, benzimidazole compounds, etc. Their amount is preferably0.15-1.5 parts by weight.

The surface treatment bath for forming a hydrophilic coating on analuminum member according to the present invention is produced byproperly diluting the above surface treatment chemical. Accordingly,percentage of the components in the bath are substantially the same asdescribed above. The concentration of the surface treatment bath isusually adjusted so as to be able to provide a hydrophilic coating of0.05-0.5 g/m² on an aluminum plate by dipping, spraying, brushing, etc.In general, the concentration of solid components in the bath may be10-200 g/l. If some of the components decrease unproportionally, theyshould be supplemented in order to maintain the percentage of eachcomponent at a proper level.

Next, the method of surface treatment according to the present inventionwill be explained below.

Before forming a coating layer with the surface treatment chemical, adegreasing treatment is usually conducted. The degreasing treatment maybe conducted by using such solvents as trichloroethylene,perchloroethylene, gasoline, n-hexane, etc., or alkali solutions ofsodium hydroxide, sodium carbonate, sodium silicate, sodium phosphate,etc.

After degreasing, a chemical treatment is conducted to form acorrosion-resistant layer on a degreased aluminum member. Thecorrosion-resistant layer can be obtained by a chromate treatment. Thechromate treatment is conducted with a treatment liquid containingchromic acid and sulfuric acid, nitric acid, fluoric acid, phosphoricacid, etc. and proper additives.

The chromate treatment is catagorized into two groups; a phosphoricchromate treatment using phosphoric acid as an inorganic acid, and achromium chromate treatment using the other acids. From the viewpoint ofcorrosion resistance, the latter is better. The chromate treatment canbe conducted by immersion in a treatment liquid, or spraying thetreatment liquid. However, to fit exchanger's fins having complicatedshapes, an immersion method is easier. The corrosion-resistant layerobtained by the chromate treatment has a Cr content of 3-50 mg/m². Whenit is less than 3 mg/m², the layer does not have sufficient corrosionresistance. On the other hand, when it exceeds 50 mg/m², its reactionwith the hydrophilic layer takes place, resulting in the deteriorationof its hydrophilic nature. The aluminum member formed with thecorrosion-resistant layer is then washed with water. This is preferablydone with flowing water for 10-30 seconds or so.

In addition to the above chromate treatment, a chemical treatment canalso be conducted by using a zirconium treating agent. The zirconiumtreating agent may be a mixture of polyacrylic acid and zirconiumfluoride, etc. A layer produced by this zirconium treatment agent has aZr content of 0.1-40 mg/m². Like the Cr content, when the Zr content isless than 0.1 mg/m², sufficient corrosion resistance cannot be obtained.and when it exceeds 40 mg/m², the hydrophilic nature rather decreases.When the zirconium treatment is conducted after the chromate treatment,larger effects can be obtained.

Better corrosion resistance can also be obtained by conducting coatingof a phenol resin primer after the degreasing. For this purpose, aresol-type water-soluble phenol resin (prepolymer of phenol and formalinproduced in the presence of an alkali catalyst) is preferable, and, forinstance, Resitop PL-2761, PL-2717 manufactured by Gun Ei ChemicalIndustry Co., Ltd. and Tamanol 721, 722 of Arakawa Chemical Inc., etc.may be used. The phenol resin primer may contain a melamine resin as asubstitute for a phenol resin. A preferable melamine resin iswater-soluble one, to which methyl groups, ethyl groups and/or butylgroups are introduced. The content of the melamine resins is 50 weight %or less to 50-100 weight % of the phenol resin. In addition, to increasethe workability, such as bending of the coated aluminum member, andapplicability of the surface treatment chemical, acrylic resins, etc.may be added.

The phenol resin primer layer is heated at 180°-280° C. for 10 seconds -1 minute after application. The resulting primer layer is preferably0.5-2 g/m². When it is less than 0.5 g/m², it does not have sufficientcorrosion resistance, and when it exceeds 2 g/m², not only heat exchangeefficiency decreases, but also the production cost becomes high.

The surface treatment chemical of the present invention is dilutedproperly as a bath, and applied to the aluminum surface subjected todegreasing and then to the above chemical treatment. This can be done bya roll-coating method, a bar-coating method, an immersion method, aspraying method, a brushing method, etc. For instance, in the case of aroll-coating method, the hydrophilic coating can be obtained by dryingat 150°-240° C. for 10 seconds - 1 minute after application. Theresulting hydrophilic coating is 0.05-0.5 g/m². When it is less than0.05 g/m², it does not have sufficient hydrophilic nature, and when itexceeds 0.5 g/m², the production cost becomes high without providing thecorrespondingly increased effects.

Another surface treatment chemical according to the present inventioncomprises, on a solid basis, 5-25 parts by weight of a sodium saltand/or a potassium salt of carboxymethylcellulose, 25-50 parts by weightof an ammonium salt of carboxymethylcellulose, 25-70 parts by weight ofN-methylol acrylamide, and further, per 100 parts by weight of a totalof the above components, 1.5-15 parts by weight of polyacrylic acid and0.6-9 parts by weight (as Zr) of a zirconium compound.

The sodium salt and/or the potassium salt of carboxymethylcellulose, theammonium salt of carboxymethylcellulose, and N-methylol acrylamide maybe the same as described above.

Polyacrylic acid contributes to increase the alkali resistance and thecorrosion resistance of the resulting hydrophilic coating. The contentof the polyacrylic acid is 1.5-15 parts by weight per 100 parts byweight of the sodium salt and/or the potassium salt ofcarboxymethylcellulose + the ammonium salt of carboxymethylcellulose +N-methylol acrylamide. When it is less than 1.5 parts by weight,sufficient effect of increasing the corrosion resistance cannot beachieved. When it exceeds 15 parts by weight, the hydrophilic naturedecreases. The preferred content of the polyacrylic acid is 2-8 parts byweight. Incidentally, in the present invention, the polyacrylic acid isnot restricted to that having a repeating structure unit represented bythe formula: [CH₂ CH-COOH]_(n), but it may include any polyacrylic acidhaving substituents such as methyl groups, etc.

As zirconium compounds, one or more water-soluble oxides, halides,oxyacid salts, organic acid salts or complex salts which are stable inthe treatment solution, may be used alone or in combination.Specifically, they are oxides or their related compounds, such as ZrO₂,ZrO₂ ·xH₂ O, H₂ ZrO₃ or M₂ ZrO₃ (zirconium acid or its salt), ZrO₃ ·2H₂O, K₄ ZrO₄ ·2H₂ O₂ ·2H₂ O (peroxozirconium acid or its salt), etc.:halides such as ZrCl₂, ZrBr₂, ZrI₂, ZrCl₃, ZrBr₃, ZrI₃, ZrF₄, ZrCl₄,ZrBr₄, ZrI₄, BrOCl₂ ·8H₂ O, Zr₂ O₃ Cl₂, etc.; oxyacid salts such asZr(NO₃)₄ ·5H₂ O, ZrO(NO₃)₂ ·2H₂ O, Zr(SO₄)₂, Zr(SO₄)₂ ·4H₂ O, ZrO(SO₄),ZrO(H₂ PO₄)₂, ZrP₂ O₇, ZrSiO₄, ZrCO₄ · ZrO₂ ·8H₂ O (basic zirconiumcarbonate); organic acid salts such as Zr(CH₃ CO₂)₄, ZrO(CH₃ CO₂)₂,etc.; and acids or their complex salts such as H₂ ZrF₆ or M₂ ZrF₆(hexafluorozirconium(IV) acid or its salt), H₄ ZrF₈ or M₄ ZrF₈(octafluorozirconium(IV) acid or its salt), H₄ [Zr (C₂ O₄)₄ ] or M₄ [Zr(C₂ O₄)₄ ] tetraoxalatozirconium (IV) acid or its salt), (C₅ H₅)₂ ZrBr₂,etc. Incidentally, in the above formulae, M represents an alkali metal.Particularly preferred zirconium compounds are acids or their complexsalts such as hexafluorozirconium acid or its salt, octafluorozirconiumacid or its salt, tetraoxalatozirconium acid or its salt, oxyacid saltssuch as basic zirconium carbonate, zirconium nitrate, zirconium sulfate,etc.

The content of the zirconium compound as Zr is 0.6-9 parts by weight per100 parts by weight of (the sodium and/or the potassium salt ofcarboxymethylcellulose + the ammonium salt of carboxymethylcellulose +N-methylol acrylamide). When it is less than 0.6 parts by weight,sufficient effects of increasing alkali resistance and corrosionresistance cannot be achieved, and when it exceeds 9 parts by weight,the viscosity of the treatment solution increases, making the coatingoperation difficult. The preferred amount of the zirconium compound is1-5 parts by weight.

The polyacrylic acid and the zirconium compound provide a synergisticeffect, so that the addition of both compounds in proper proportionsprovides an unexpectedly large effects. In general, a weight ratio ofpolyacrylic acid/Zr in the zirconium compound is preferably 0.17-25. Inthis range, sufficient effect of increasing corrosion resistance andalkali resistance can be achieved. The preferred weight ratio ofpolyacrylic acid/Zr in the zirconium compound is 0.4-8.

In this surface treatment chemical, surfactants, anti-mold agents,antiseptics, fluoric acid, etc. may be added in addition to the aboveindispensable components. With respect to the surfactants, the anti-moldagents and the antiseptics, the same materials as described above may beused.

Fluoric acid has a function to increase the film-forming properties,corrosion resistance, and alkali resistance of the resulting coatinglayer when the surface treatment chemical is directly applied to analuminum surface without forming a corrosion-resistant layer afterdegreasing. The amount of fluoric acid is 2.5-100 ppm in a treatmentsolution having such a concentration as to provide a hydrophilic coatingof 0.05-0.5 g/m² on a dry basis. When it is less than 2.5 ppm,sufficient effect cannot be obtained, and when it exceeds 100 ppm,correspondingly increased effects cannot be obtained.

This surface treatment chemical may be diluted similarly to provide asurface treatment bath, which may be applied to an aluminum memberessentially in the same manner as described above except that theformation of corrosion-resistant layer is not necessary.

Briefly speaking, after degreasing, an aluminum member is directlycoated with this surface treatment chemical. However, when highcorrosion resistance and alkali resistance are required, a chemicaltreatment may be conducted after degreasing to form acorrosion-resistant layer. This corrosion-resistant layer can beobtained similarly by a chromate treatment. Further, after degreasing, aprimer of a phenol resin, an epoxy resin, etc. may be applied to furtherincrease the corrosion resistance.

The application of this surface treatment chemical to the degreasedaluminum surface which may be coated with a corrosion-resistant layer,if necessary, can be conducted in the same manner as described above.

The present invention will be explained in further detail by means ofthe following Examples.

EXAMPLES 1-5

Each of aluminum plates is degreased and then coated with a zirconiumsurface treatment agent (Alodine 1690/1691, manufactured by Nippon PaintCo., Ltd.) by a bar coating method, and then dried at 150° C. for 15seconds to form a corrosion-resistant coating having 5 mg/m² of Zrcontent.

Each of the coated aluminum plates is then coated with an aqueoussurface treatment solution containing a sodium salt and an ammonium saltof carboxymethylcellulose and N-methylol acrylamide in the compositionshown in Table 1 by a bar coating method, and then dried at 240° C. for30 seconds to form a hydrophilic coating. Each hydrophilic coating is0.2 g/m². Incidentally, the above hydrophilic surface treatment solutioncontains 5 parts by weight of sodium alkyldiphenylether disulfonate as asurfactant, and 0.25 parts by weight of a benzimidazole compound and0.25 parts by weight of a nitrogen-containing sulfur compound both asanti-mold agents, per 100 parts by weight of the above indispensablecomponents.

Each of the resulting hydrophilic coatings is tested with respect toodor, water dissolution resistance, contact angle of water (durabilityof hydrophilic nature) and corrosion resistance. The test procedures andthe evaluation standards of test results are as follows:

(1) Odor test

Each aluminum plate formed with a hydrophilic coating (hereinafterreferred to simply as "sample") is tested with respect to odor bydirectly smelling. The odor is classified as follows:

Excel.: No odor at all

Good: Only slight odor

Fair: Medium odor

Poor: Strong odor

(2) Water dissolution resistance

Each sample is dipped in running water for 24 hours, and the weight ofthe coating is measured before and after dipping to determine a waterdissolution ratio by the following equation: ##EQU1##

The evaluation standards of water dissolution resistance are as follows:

Excel.: less than 10%:

Good: 10% or more and less than 30%;

Fair: 30% or more and less than 50%;

Poor: 50% or more.

3 Test cf contact angle of water (Test of durability of hydrophilicnature)

Each sample is subjected to five cycles of treatments, each of whichconsists of keeping it in contact with running water (5 l/hr) for 17hours and drying it at 80° C. for 7 hours. After that, 5 μl of deionizedwater is dropped onto a flat surface of each sample held horizontally tomeasure a contact angle Q of a water droplet by a goniometer. Thecontact angle Q is classified into the following categories:

Excel.: Q<20°

Good: 20°≦Q<30°

Fair: 30°≦Q<40°

Poor: 40°≦Q

(4) Corrosion resistance test (Salt Spray Test: SST)

According to JIS Z 2371, each sample is sprayed with a sodium chlorideaqueous solution for 500 hours to measure the coating's resistance tosalt water. The corrosion resistance is evaluated by a ratio of whiterust area. The evaluation is conducted by the following standards:

Ratio of white rust area

Excel.: 0%:

Good: More than 0% and less than 10%;

Fair: 10% or more and less than 50%;

Poor: 50% or more.

The test results are shown in Table 1.

EXAMPLE 6

A hydrophilic coating is formed under the same conditions as in Example1 except for changing the Zr content of the zirconium coating by Alodine1690/1691 to 0.1 mg./², and using a hydrophilic surface treatmentsolution having the composition as shown in Table 1. The same tests arecarried out. The results are shown in Table 1.

EXAMPLE 7

Example 6 is repeated except for changing the Zr content of thezirconium coating by Alodine 1690/1691 to 40 mg/m² to form a hydrophiliccoating, and the same tests are carried out. The results are shown inTable 1.

EXAMPLES 8-10

A Zr corrosion-resistant coating having a Zr content of 2 mg/m² isformed by Alodine 1690/1691 as in Example 6, and a corrosion-resistantchromate coating having a Cr content of 3 mg/m² (Example 8), 20 mg/m²(Example 9) and 50 mg/m² (Example 10), respectively is then formed byconducting a phosphoric chromate treatment with Alodine 407/47(manufactured by Nippon Paint Co., Ltd.). Formed thereon is ahydrophilic coating by a hydrophilic surface treatment solution havingthe composition shown in Table 1. The test results are shown in Table 1.

EXAMPLES 11-13

Examples 8-10 are repeated except for forming a chromate coating havinga Cr content of 3 mg/m² (Example 11), 20 mg/m² (Example 12) and 50 mg/m²(Example 13), respectively by Alodine 407/47 without forming a Zrcorrosion-resistant coating by Alodine 1690/1691. Formed thereon is ahydrophilic coating having the same composition as in Example 6. Thetest results are shown in Table 1.

EXAMPLES 14-16

A corrosion-resistant coating and a hydrophilic coating are formed as inExamples 11-13 except for using Alodine 600 as a chromium chromatechemical treatment agent in place of Alodine 407/47 to form a chromatecoating having a Cr content of 3 mg/m² (Example 14), 20 mg/m² (Example15) and 50 mg/m² (Example 16), respectively. The test results are shownin Table 1.

EXAMPLES 17 and 18

A primer layer of 0.5 g/m² (Example 17) and 2.0 g/m² (Example 18),respectively is formed by using NP Alcoat 450 (manufactured by NipponPaint Co., Ltd.) as a phenol resin primer paint and baked. A hydrophiliccoating of 0.2 g/m² is then formed on each primer layer by a hydrophilicsurface treatment solution having the same composition as in Example 6.The resulting hydrophilic coatings are tested as above, and the resultsare shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Composition (Parts by Weight)                                                 Example                                                                       No.  CMC-Na.sup.1                                                                        CMC-NH.sub.4.sup.2                                                                  N-MAM.sup.3                                                                        CMC.sup.4 /N-MAM                                                                       CMC-Na/CMC-NH.sub.4                            __________________________________________________________________________     1   5     25    70   0.43     0.2                                             2   12.5  37.5  50   1.0      0.33                                            3   25    50    25   3.0      0.5                                             4   5     50    45   1.22     0.1                                             5   25    25    50   1.0      1.0                                             6   12.5  37.5  50   1.0      0.33                                            7   12.5  37.5  50   1.0      0.33                                            8   12.5  37.5  50   1.0      0.33                                            9   12.5  37.5  50   1.0      0.33                                           10   12.5  37.5  50   1.0      0.33                                           11   12.5  37.5  50   1.0      0.33                                           12   12.5  37.5  50   1.0      0.33                                           13   12.5  37.5  50   1.0      0.33                                           14   12.5  37.5  50   1.0      0.33                                           15   12.5  37.5  50   1.0      0.33                                           16   12.5  37.5  50   1.0      0.33                                           17   12.5  37.5  50   1.0      0.33                                           18   12.5  37.5  50   1.0      0.33                                           __________________________________________________________________________    Properties                                                                                Water                                                             Example     Dissolution                                                                            Contact Angle                                                                         Corrosion                                        No.     Odor                                                                              Resistance                                                                             of Water                                                                              Resistance (SST)                                 __________________________________________________________________________     1      excel.                                                                            excel.   good    good                                              2      excel.                                                                            excel.   excel.  good                                              3      excel.                                                                            good     excel.  good                                              4      excel.                                                                            excel.   good    good                                              5      good                                                                              excel.   excel.  good                                              6      excel.                                                                            excel.   excel.  good                                              7      excel.                                                                            excel.   good    good                                              8      excel.                                                                            excel.   excel.  excel.                                            9      excel.                                                                            excel.   excel.  excel.                                           10      excel.                                                                            excel.   good    excel.                                           11      excel.                                                                            excel.   excel.  good                                             12      excel.                                                                            excel.   excel.  good                                             13      excel.                                                                            excel.   good    good                                             14      excel.                                                                            excel.   excel.  good                                             15      excel.                                                                            excel.   excel.  good                                             16      excel.                                                                            excel.   good    good                                             17      excel.                                                                            excel.   excel.  excel.                                           18      excel.                                                                            excel.   excel.  excel.                                           __________________________________________________________________________     Note                                                                          .sup.1 Sodium salt of carboxymethylcellulose (APP84 manufactured by           SanyoKokusaku Pulp Co., Ltd.)                                                 .sup.2 Ammonium salt of carboxymethylcellulose (DN10L manufactured by         Daicel Chemical Industries, Ltd.)                                             .sup.3 Nmethylol acrylamide (NMAM P manufactured by Soken Chemical &          Engineering Co., Ltd.)                                                        .sup.4 Total of sodium salt and ammonium salt of carboxymethylcellulose  

Example 19

A hydrophilic coating is formed in the same manner as in Example 2except for using a potassium salt of carboxymethylcellulose instead ofits sodium salt. The resulting hydrophilic coating is subjected to thesame tests. The following results are obtained.

Odor: Excellent

Water dissolution resistance: Excellent

Contact angle of water: Excellent

Corrosion resistance: Good

COMPARATIVE EXAMPLES 1-8

Each of degreased aluminum plates is provided with a corrosion-resistantzirconium coating (Zr content: 5 mg/m²) by Alodine 1690/1691, and ahydrophilic coating is formed thereon by a hydrophilic surface treatmentsolution having the composition shown in Table 2. The hydrophiliccoating of each sample is tested in the same manner as in Example 1. Theresults are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Composition (Parts by Weight)                                                 Comparative                                                                   Example                 CMC.sup.4 /                                                                           CMC-Na/                                       No.    CMC-Na.sup.1                                                                        CMC-NH.sub.4.sup.2                                                                  N-MAM.sup.3                                                                        N-MAN   CMC-NH.sub.4                                  __________________________________________________________________________    1       3    50    47   1.13    0.06                                          2       3    22    75   0.33    0.14                                          3      30    50    20   4.0     0.6                                           4      30     0    70   0.43    --                                            5      10    20    70   0.43    0.5                                           6       5    60    35   1.86    0.08                                          7      25    55    20   4.0     0.45                                          8      20     0    80   0.25    --                                            __________________________________________________________________________    Properties                                                                    Comparative  Water                                                            Example      Dissolution                                                                          Contact Angle                                                                          Corrosion                                        No.     Odor Resistance                                                                           of Water Resistance (SST)                                 __________________________________________________________________________    1       excel.                                                                             excel. fair     good                                             2       fair excel. fair     good                                             3       fair fair   excel.   good                                             4       poor excel. excel.   good                                             5       fair excel. good     good                                             6       excel.                                                                             excel. fair     good                                             7       excel.                                                                             fair   fair     good                                             8       poor excel. poor     good                                             __________________________________________________________________________     Note                                                                          .sup.1-4 Same as in Table 1.                                             

EXAMPLES 20-29

Each of degreased aluminum plates is coated with an aqueous surfacetreatment solution containing a sodium salt and an ammonium salt ofcarboxymethylcellulose, N-methylol acrylamide, polyacrylic acid and azirconium compound in the composition shown in Table 3 by a bar coatingmethod, and then dried at 240° C. for 30 seconds to form a hydrophiliccoating. Each hydrophilic coating is 0.2 g/m². Incidentally, the abovehydrophilic surface treatment solution contains 5 parts by weight ofsodium alkyldiphenylether disulfonate as a surfactant, 0.25 parts byweight of a benzimidazole compound and 0.25parts by weight of anitrogen-containing sulfur compound both as anti-mold agents, per 100parts by weight of the above indispensable components. This solution'sconcentration is adjusted such that the resulting dried coating has aweight of 0.2 g/m². In this concentration, this solution furthercontains 25 ppm of fluoric acid.

Each of the resulting hydrophilic coatings is tested with respect toodor, water dissolution resistance, contact angle of water (durabilityof hydrophilic nature), corrosion resistance and alkali resistance. Withrespect to odor, water dissolution resistance, contact angle of waterand corrosion resistance, the same test procedures as above areconducted, and the same evaluation standards are employed.

(5) Alkali resistance test

Each sample is immersed in Ridoline 53 (manufactured by Nippon PaintCo., Ltd.) as an alkali detergent solution under the conditions asdescribed below. After washing it with running water for 10 seconds, thehydrophilic coating is observed and compared with that before immersion.

    ______________________________________                                        Immersion conditions                                                          ______________________________________                                        Concentration of Ridoline 53:                                                                    3.0 weight %                                               Immersion temperature:                                                                           70° C.                                              Immersion time:    3 minutes.                                                 The evaluation standards of coating appearance are as                         follows:                                                                      Excel.:            Not swelled at all                                         Good:              Slightly swelled                                           Fair:              Swelled                                                    Poor:              Partially peeled                                           ______________________________________                                         The results are shown in Table 3.                                        

EXAMPLE 30

A hydrophilic coating is formed in the same manner as in Example 20except for using a potassium salt of carboxymethylcellulose instead ofits sodium salt. The resulting hydrophilic coating is subjected to thesame tests. The results are shown in Table 3.

EXAMPLE 31

A hydrophilic coating is formed in the same manner as in Example 20except for using (NH₄)₃ ZrOH(CO₃)₃ ·2H₂ O instead of H₂ ZrF₆. Theresulting hydrophilic coating is similarly tested. The results are shownin Table 3.

EXAMPLES 32-36

Each of aluminum plates degreased in the same manner as in Example 20 isprovided with a phosphoric chromate coating having a Cr content of 3mg/m², 20 mg/m² and 50 mg/m², respectively with Alodine 407/47(manufactured by Nippon Paint Co., Ltd.). Formed thereon is ahydrophilic coating by a hydrophilic surface treatment solution havingthe composition shown in Table 3. The test results are shown in Table 3.

EXAMPLES 37-41

A chromate coating having a Cr content of 3 mg/m², 20 mg/m² and 50mg/m², respectively is formed in the same manner as in Examples 32-36except for using Alodine 600 as a chromium chromate chemical treatmentagent instead of Alodine 407/47, and a hydrophilic coating having thesame composition as in Examples 32-36 is formed thereon. The testresults are shown in Table 3.

EXAMPLES 42-45

Each of aluminum plates degreased in the same manner as in Example 20 iscoated with NP Alcoat 450 (manufactured by Nippon Paint Co., Ltd.) as aphenol resin primer paint, and baked to form a primer layer of 0.5 g/m²and 2.0 g/m², respectively. Next, a hydrophilic coating of 0.2 g/m² isformed with a hydrophilic surface treatment solution having thecomposition as shown in Table 3. The results are shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                     Composition of Hydrophilic Coating (Parts by Weight)                                                          Zr                                                                            Com-                         Undercoat                         CMC-Na         pound                        Example     Weight                                                                             CMC.sup.1 -                                                                       CMC.sup.2 -                                                                       CMC.sup.3 -                                                                            or Ka/                                                                              CMC.sup.5 /                                                                            (as Zr)                                                                            PAA/                    No.  Type   (mg/m.sup.2)                                                                       Na  Ka  NH.sub.4                                                                          N-MAM.sup.4                                                                        CMC-NH.sub.4                                                                        N-MAM                                                                              PAA.sup.6                                                                         A.sup.7                                                                         B.sup.8                                                                          Zr                      __________________________________________________________________________    20   Only   --   12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Degreasing                                                               21   Only   --   12.5                                                                              --  37.5                                                                              50   0.33  1.0  1.5 8.8                                                                             -- 0.                           Degreasing                                                               22   Only   --   12.5                                                                              --  37.5                                                                              50   0.33  1.0  15  0.88                                                                            -- 17                           Degreasing                                                               23   Only   --   12.5                                                                              --  37.5                                                                              50   0.33  1.0  1.5 0.88                                                                            -- 1.7                          Degreasing                                                               24   Only   --   12.5                                                                              --  37.5                                                                              50   0.33  1.0  15  8.8                                                                             -- 1.7                          Degreasing                                                               25   Only   --   5   --  25  70   0.2   0.43 15  0.88                                                                            -- 17                           Degreasing                                                               26   Only   --   5   --  25  70   0.2   0.43 15  8.8                                                                             -- 1.7                          Degreasing                                                               27   Only   --   25  --  50  25   0.5   3.0  1.5 0.88                                                                            -- 1.7                          Degreasing                                                               28   Only   --   5   --  50  45   0.1   1.22 15  0.88                                                                            -- 17                           Degreasing                                                               29   Only   --   25  --  25  50   1.0   1.0  3.75                                                                              2.2                                                                             -- 1.7                          Degreasing                                                               30   Only   --   --  12.5                                                                              37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Degreasing                                                               31   Only   --   12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              --                                                                              2.2                                                                              1.7                          Degreasing                                                               32   Phosphoric                                                                           3    12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Chromate                                                                      Alodine                                                                       407/47                                                                   33   Phosphoric                                                                           20   12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Chromate                                                                      Alodine                                                                       407/47                                                                   34   Phosphoric                                                                           50   12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Chromate                                                                      Alodine                                                                       407/47                                                                   35   Phosphoric                                                                           20   --  12.5                                                                              37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Chromate                                                                      Alodine                                                                       407/47                                                                   36   Phosphoric                                                                           20   12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              --                                                                              2.2                                                                              1.7                          Chromate                                                                      Alodine                                                                       407/47                                                                   37   Chromium                                                                             3    12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Chromate                                                                      Alodine 600                                                              38   Chromium                                                                             20   12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Chromate                                                                      Alodine 600                                                              39   Chromium                                                                             50   12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Chromate                                                                      Alodine 600                                                              40   Chromium                                                                             20   --  12.5                                                                              37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Chromate                                                                      Alodine 600                                                              41   Chromium                                                                             20   12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              --                                                                              2.2                                                                              1.7                          Chromate                                                                      Alodine 600                                                              42   Phenol resin                                                                         500  12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Primer                                                                        Alcoat 450                                                               43   Phenol resin                                                                         2000 12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Primer                                                                        Alcoat 450                                                               44   Phenol resin                                                                         500  --  12.5                                                                              37.5                                                                              50   0.33  1.0  3.75                                                                              2.2                                                                             -- 1.7                          Primer                                                                        Alcoat 450                                                               45   Phenol resin                                                                         500  12.5                                                                              --  37.5                                                                              50   0.33  1.0  3.75                                                                              --                                                                              2.2                                                                              1.7                          Primer                                                                        Alcoat 450                                                               __________________________________________________________________________    Properties                                                                                      Water                                                       Example           Dissolution                                                                         Contact Angle                                                                              Corrosion                                                                              Alkali                          No.     Odor      Resistance                                                                          of Water     Resistance (SST)                                                                       Resistance                      __________________________________________________________________________    20      excel.    excel.                                                                              excel.       good     excel.                          21      excel.    excel.                                                                              excel.       good     good                            22      excel.    excel.                                                                              good         good     good                            23      excel.    excel.                                                                              excel.       good     good                            24      excel.    excel.                                                                              good         good     excel.                          25      good      excel.                                                                              good         good     good                            26      good      excel.                                                                              good         good     excel.                          27      good      good  good         good     good                            28      excel.    excel.                                                                              good         good     good                            29      good      excel.                                                                              excel.       good     excel.                          30      excel.    excel.                                                                              excel.       good     excel.                          31      excel.    excel.                                                                              excel.       good     excel.                          32      excel.    excel.                                                                              excel.       good     excel.                          33      excel.    excel.                                                                              excel.       excel.   excel.                          34      excel.    excel.                                                                              good         excel.   excel.                          35      excel.    excel.                                                                              excel.       excel.   excel.                          36      excel.    excel.                                                                              excel.       excel.   excel.                          37      excel.    excel.                                                                              excel.       good     excel.                          38      excel.    excel.                                                                              excel.       excel.   excel.                          39      excel.    excel.                                                                              good         excel.   excel.                          40      excel.    excel.                                                                              excel.       excel.   excel.                          41      excel.    excel.                                                                              excel.       excel.   excel.                          42      excel.    excel.                                                                              excel.       excel.   excel.                          43      excel.    excel.                                                                              excel.       excel.   excel.                          44      excel.    excel.                                                                              excel.       excel.   excel.                          45      excel.    excel.                                                                              excel.       excel.   excel.                          __________________________________________________________________________     Note                                                                          .sup.1 Sodium salt of carboxymethylcellulose (APP84 manufactured by           SanyoKokusaku Pulp Co., Ltd.)                                                 .sup.2 Potassium salt of carboxymethylcellulose (acidtype CMC neutralized     with KOH to show pH 6, manufactured by Daicel Chemical Industries, Ltd.)      .sup.3 Ammonium salt of carboxymethylcellulose (DN10L, manufactured by        Daicel Chemical Industries, Ltd.)                                             .sup.4 Nmethylol acrylamide (NMAM P, manufactured by Soken Chemical &         Engineering Co., Ltd.)                                                        .sup.5 Total of sodium or potassium salt and ammonium salt of                 carboxymethylcellulose                                                        .sup.6 Polyacrylate acid (AC10L, manufactured by Nihon Junyaku Co., Ltd.)     .sup.7 H.sub.2 ZrF.sub.6 (manufactured by Morita Kagaku Co., Ltd.)            .sup.8 (NH.sub.4).sub.3 ZrOH(CO.sub.3).sub.3.2H.sub.2 O                  

COMPARATIVE EXAMPLES 9-14

Each of aluminum plates degreased in the same manner as in Example 20 isprovided with a hydrophilic coating with a hydrophilic surface treatmentsolution having the composition as shown in Table 4. The hydrophiliccoating of each sample is subjected to the same tests as in Example 20.The results are shown in Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Comparative                                                                           Undercoat  Composition of Hydrophilic Coating (Parts by Weight)       Example       Weight                 CMC-Na/                                                                             CMC.sup.4 /                                                                             H.sub.2 ZrF.sub.6.sup                                                         .6   PAA/                No.     Type  (mg/m.sup.2)                                                                       CMC-Na.sup.1                                                                         CMC-NH.sub.4.sup.2                                                                  N-MAM.sup.3                                                                        CMC-NH.sub.4                                                                        N-MAM PAA.sup.5                                                                         (as                                                                                Zr)                 __________________________________________________________________________     9      Only  --   12.5   37.5  50   0.33  1.0   3.75                                                                              0    --                          Degreasing                                                            10      Only  --   12.5   37.5  50   0.33  1.0   0   2.2  --                          Degreasing                                                            11      Only  --   12.5   37.5  50   0.33  1.0   1.0 8.8  0.11                        Degreasing                                                            12      Only  --   12.5   37.5  50   0.33  1.0   15  0.44 34                          Degreasing                                                            13      Only  --   12.5   37.5  50   0.33  1.0   1.5 11.0 0.14                        Degreasing                                                            14      Only  --   12.5   37.5  50   0.33  1.0   20  0.88 22.7                        Degreasing                                                            __________________________________________________________________________    Properties                                                                    Comparative          Water                                                    Example              Dissolution                                                                         Contact Angle Corrosion                                                                              Alkali                      No.        Odor      Resistance                                                                          of Water      Resistance (SST)                                                                       Resistance                  __________________________________________________________________________     9         excel.    excel.                                                                              excel.        fair     fair                        10         excel.    excel.                                                                              excel.        poor     excel.                      11         excel.    excel.                                                                              excel.        fair     good                        12         excel.    excel.                                                                              good          fair     fair                         13*       --        --    --            --       --                          14         excel.    excel.                                                                              fair          good     good                        __________________________________________________________________________     Note                                                                           *Gelatin takes place.                                                        .sup.1 Sodium salt of carboxymethylcellulose as in Table 3                    .sup.2 Ammonium salt of carboxymethylcellulose as in Table 3                  .sup.3 Nmethylol acrylamide as in Table 3                                     .sup.4 Total of sodium salt and ammonium salt of carboxymethylcellulose       .sup.5 Polyacrylic acid as in Table 3                                         .sup.6 As in Table 3                                                     

As described above, the hydrophilic coating formed by the surfacetreatment chemical according to the present invention has not only goodhydrophilic nature, water dissolution resistance and corrosionresistance, but also extremely reduced odor. In addition, it isexcellent in alkali resistance when containing both of polyacrylic acidand a zirconium compound. Therefore, it is highly suitable for ahydrophilic treatment of aluminum fins of heat exchangers, etc.

The present invention has been described by Examples, but it should benoted that any modifications are possible unless they deviate from thescope of the present invention defined by the claims attached hereto.

What is claimed is:
 1. A surface treatment chemical for forming ahydrophilic coating comprising, on a solid basis of 100 of, 5-25 partsby weight of a sodium salt and/or a potassium salt ofcarboxymethylcellulose, 25-50 parts by weight of an ammonium salt ofcarboxymethylcellulose, and 25-70 parts by weight of N-methylolacrylamide.
 2. The surface treatment chemical for forming a hydrophiliccoating according to claim 1, wherein a weight ratio of said sodium saltand/ or said potassium salt of carboxymethylcellulose to said ammoniumsalt of carboxymethylcellulose is 0.1-1.0.
 3. The surface treatmentchemical for forming a hydrophilic coating according to claim 2, whereina weight ratio of total of said sodium salt and/or said potassium saltof carboxymethylcellulose and said ammonium salt ofcarboxymethylcellulose to said N-methylol acrylamide is 0.43-3.0.
 4. Asurface treatment bath for forming a hydrophilic coating on an aluminummember comprising, on a solid basis of 100 parts, 5-25 parts by weightof a sodium salt and/or a potassium salt of carboxymethylcellulose,25-50 parts by weight of an ammonium salt of carboxymethylcellulose, and25-70 parts by weight of N-methylol acrylamide.
 5. The surface treatmentbath for forming a hydrophilic coating on an aluminum member accordingto claim 4, wherein a weight ratio of said sodium salt and/ or saidpotassium salt of carboxymethylcellulose to said ammonium salt ofcarboxymethylcellulose is 0.1-1.0.
 6. The surface treatment bath forforming a hydrophilic coating on an aluminum member according to claim5, wherein a weight ratio of total of said sodium salt and/or saidpotassium salt of carboxymethylcellulose and said ammonium salt ofcarboxymethylcellulose to said N-methylol acrylamide is 0.43-3.0.
 7. Asurface treatment chemical for forming a hydrophilic coating comprising,on a solid basis of 100 parts, 5-25 parts by weight of a sodium saltand/or a potassium salt of carboxymethylcellulose, 25-50 parts by weightof an ammonium salt of carboxymethylcellulose, 25-70 parts by weight ofN-methylol acrylamide, and further, per 100 parts by weight of (saidsodium salt and/or said potassium salt of carboxymethylcellulose + saidammonium salt of carboxymethylcellulose + said N-methylol acrylamide),1.5-15 parts by weight of polyacrylic acid and 0.6-9 parts by weight (asZr) of a zirconium compound.
 8. The surface treatment chemical forforming a hydrophilic coating according to claim 7, wherein a weightratio of said sodium salt and/ or said potassium salt ofcarboxymethylcellulose to said ammonium salt of carboxymethylcelluloseis 0.1-1.0.
 9. The surface treatment chemical for forming a hydrophiliccoating according to claim 7 or 8, wherein a weight ratio of total ofsaid sodium salt and/or said potassium salt of carboxymethylcelluloseand said ammonium salt of carboxymethylcellulose to said N-methylolacrylamide is 0.43-3.0.
 10. The surface treatment chemical for forming ahydrophilic coating according to claim 7, wherein a weight ratio ofpolyacrylic acid to said zirconium compound (as Zr) is 0.17-25.
 11. Thesurface treatment chemical for forming a hydrophilic coating accordingto claim 7, wherein said polyacrylic acid is 2-8 parts by weight andsaid zirconium compound is 1-5 parts by weight (as Zr), per 100 parts byweight of a total of 9-16 parts by weight of said sodium salt and/orsaid potassium salt of carboxymethylcellulose, 30-45 parts by weight ofsaid ammonium salt of carboxymethylcellulose and 39-61 parts by weightof said N-methylol acrylamide.
 12. The surface treatment chemical forforming a hydrophilic coating according to claim 11, wherein a weightratio of said sodium salt and/or said potassium salt ofcarboxymethylcellulose to said ammonium salt of carboxymethylcelluloseis 0.2-0.53, and a weight ratio of total of said sodium salt and/or saidpotassium salt of carboxymethylcellulose and said ammonium salt ofcarboxymethylcellulose to N-methylol acrylamide is 0.64-1.56.
 13. Thesurface treatment chemical for forming a hydrophilic coating accordingto claim 10, wherein a weight ratio of said polyacrylic acid to saidzirconium compound (as Zr) is 0.4-8.
 14. A surface treatment bath forforming a hydrophilic coating on an aluminum member comprising, on asolid basis of 100 parts, 5-25 parts by weight of a sodium salt and/or apotassium salt of carboxymethylcellulose, 25-50 parts by weight of anammonium salt of carboxymethylcellulose, 25-70 parts by weight ofN-methylol acrylamide, and further, per 100 parts by weight of (saidsodium salt and/or said potassium salt of carboxymethylcellulose + saidammonium salt of carboxymethylcellulose + said N-methylol acrylamide),1.5-15 parts by weight of polyacrylic acid and 0.6-9 parts by weight (asZr) of a zirconium compound.
 15. The surface treatment bath for forminga hydrophilic coating on an aluminum member according to claim 14,wherein a weight ratio of said sodium salt and/ or said potassium saltof carboxymethylcellulose to said ammonium salt ofcarboxymethylcellulose is 0.1-1.0.
 16. The surface treatment bath forforming a hydrophilic coating on an aluminum member according to claim14 or 15, wherein a weight ratio of total of said sodium salt and/orsaid potassium salt of carboxymethylcellulose and said ammonium salt ofcarboxymethylcellulose to said N-methylol acrylamide is 0.43-3.0. 17.The surface treatment bath for forming a hydrophilic coating on analuminum member according to claim 14, wherein a weight ratio ofpolyacrylic acid to said zirconium compound (as Zr) is 0.17-25.
 18. Thesurface treatment bath for forming a hydrophilic coating on an aluminummember according to claim 14, wherein said polyacrylic acid is 2-8 partsby weight and said zirconium compound is 1-5 parts by weight (as Zr),per 100 parts by weight of a total of 9-16 parts by weight of saidsodium salt and/or said potassium salt of carboxymethylcellulose, 30-45parts by weight of said ammonium salt of carboxymethylcellulose and39-61 parts by weight of said N-methylol acrylamide.
 19. The surfacetreatment bath for forming a hydrophilic coating on an aluminum memberaccording to claim 18, wherein a weight ratio of said sodium salt and/orsaid potassium salt of carboxymethylcellulose to said ammonium salt ofcarboxymethylcellulose is 0.2-0.53, and a weight ratio of total of saidsodium salt and/or said potassium salt of carboxymethylcellulose andsaid ammonium salt of carboxymethylcellulose to N-methylol acrylamide is0.64-1.56.
 20. The surface treatment bath for forming a hydrophiliccoating on an aluminum member according to claim 17, wherein a weightratio of said polyacrylic acid to said zirconium compound (as Zr) is0.4-8.